Descriptions

Managing cattle to disseminate seeds of desirable plants, or alternatively, to restrict
weed seed contamination on rangelands is of interest to managers. Four experiments were
conducted to determine effects of ruminant digestion on germination of ingested seeds. A
number of plant species representing a variety of seed size and seed coat hardness were
subjected to in vitro digestion. Experiment one was conducted to determine effect of
varying lengths of digestion time on seed germination. Seed germination varied by plant
species in response to length of digestion. Germination of large soft-coated seeds, such as
bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. & Smith Goldar) and basin
wildrye (Elymus cinereus Scribn & Merril Magnar), was reduced to 0%. Smaller grass
seeds, such as Sherman big bluegrass (Poa secunda Presl. Sherman), survived but
germination declined following 24-hour, 48-hour, and 72-hour digestion. Experiment two
examined effect of different stages of ruminant digestion on seed germination. The
combination of Stage I (rumen-simulated digestion) and Stage II (abomasal-simulated
digestion) resulted in greatest seed mortality. Two water treatments were included to
evaluate the effects of high temperatures (39°C), moisture uptake, and lack of oxygen.
Water + O₂ and Water + CO₂ reduced germination, however not as much as Stage I and
Stage II treatments. The third experiment determined effects of diet quality on seed
germination. Seeds digested in rumen fluid collected from steers fed a 72% corn concentrate diet resulted in 0% germination for all species. Grass seed germination was low for seeds digested in rumen fluid collected from steers fed a forage diet. Whitetop (Cardaria draba (L.) Hand.) germination was 24% and 28% for 35-hour and 59-hour roughage treatment, respectively, and germination was 0% for 35-hour and 59-hour concentrate treatments. Germination of water-only treatments for most species was reduced in comparison to the control treatment, but was greater than remaining treatments. Experiment four evaluated germination of seeds exposed to in situ versus in vitro digestion. In situ digestion resulted in lower seed germination than in vitro digestion for all species examined. Large, soft grass seeds may not be suitable candidates for reseeding rangelands. However, it is important for managers to recognize that cattle may distribute viable weed seeds in feces. Confining cattle or supplementing with high concentrate diets may help prevent spread of weedy species.